This invention relates to plastic injection molding equipment, and in particular to a core pin for use in plastic injection molds for forming a hole through a part as it is formed in the mold.
Conventional core pins are used in plastic injection dies when holes or small depressions are desired in the molded part. In order to accomplish this function the core pin projects into the cavity and prevents the plastic from filling the area occupied by the core pin. If a hole is desired completely through the molded part the core pin must seat tightly against the opposing face of the die.
The core pin is the accepted means of accomplishing this task. However, inasmuch as the core pin is a fixed length when mounted in the die there are certain limitations, particularly when it is used to form a hole completely through the part. The fit of the core pin is critical. Excess length will damage the die and/or the core pin. On the other hand, excess clearance will cause flash, giving a poorly formed or entirely closed hole.
Due to temperature changes within the die during operation, many dimensions and clearances change as the die reaches operating temperature. Not only can this cause flashing at full temperature, but it may damage the pin if the die is tightly clamped at ambient temperature.
All dies show slight dimensional change after long service from pressure and wear. This dimensional change frequently requires refitting or shimming the core pins to acceptable sealing functions.
In some applications it is desirable to use a removable insert for accomplishing the function of readily changing a logo, or the like. When removable inserts are used which have a sealing core pin, the clearance may vary slightly from insert to insert or because of clearances allowed for installation of the insert sections.
The usual result of these complications is that flashing occurs around the end of the intended hole. This flashing must be removed, which task often requires a secondary machining operation.
It is the general object of the present invention to provide a compensating core pin which automatically compensates for dimensional changes due to wear, temperature fluctuations, and variations in removable inserts.
Another object is to provide a core pin which is not required to be fit at close tolerances, but rather will automatically adjust to zero clearance in use.
Another object is to provide such a core pin in which the installation is simple and straightforward for the tool and die maker.
A further object is to provide such a core pin requiring only state of the art manufacturing skill.
These and other objects and advantages of the present invention, and the manner in which they are achieved, will become apparent in the following specification and claims.